The present invention refers to an assembly for generating milk foam and for heating milk, comprising a milk supply container, a steam generator and a mixing element.
Such assemblies are used particularly in espresso coffee machines. Thereby, the milk foam is required first and foremost for cappuccino coffee, while heated milk can be used both for preparing white coffee and hot milk beverages.
For generating milk foam, a plurality of so-called emulsifying devices are known in the art. Usually, they comprise a steam inlet channel opening into a suction chamber. The suction chamber is connected to and communicates with both a milk supply channel and an air supply channel. By means of the steam flowing through the suction chamber, a low pressure zone is generated therein, with the result that milk is sucked into the suction chamber through the milk supply channel and air is sucked into the suction chamber through the air supply channel. This steam/air/milk-mixture is brought into a turbulent flow in a subsequent emulsifying chamber, resulting in a hot emulsion consisting of milk and air.
Emulsifying devices of the kind described above are disclosed, for example, in the documents EP 0 195 750 and EP 0 755 767. However, these emulsifying devices are not suitable for heating milk that could be used for preparing white coffee or a hot milk beverage. The reason is that the milk is compellingly foamed by these devices, a fact that is not desired in preparing white coffee or a hot milk beverage. Thus, for heating milk, such coffee machines usually comprise a separate steam outlet pipe having a steam outlet nozzle located at the end thereof. Such a steam outlet pipe is immersed directly into the cup or mug containing the milk to be heated such that the steam flowing out of the nozzle into the cup or mug heats the milk contained therein.
It is understood that this method is relatively cumbersome and the operator of the coffee machine hardly can estimate the actual temperature of the milk, resulting in a milk beverage that is usually either too hot or not hot enough. Moreover, in a machine having an external steam outlet, the danger exists that the operator may be injured by the hot steam. Finally, an external steam outlet is hard to clean, particularly because milk deposits remain mainly at the outside of the steam outlet nozzle; it is even possible that, after the steam having been shut down, milk is sucked into the steam outlet from where it hardly can be removed.
Thus, it is an object of the present invention to provide an assembly for generating milk foam, comprising a milk supply container, a steam generator and a mixing element, that is equally suitable for heating milk.
To meet this and other objects, the present invention provides an assembly for generating milk foam and for heating milk, comprising a milk supply container, a steam generator and a mixing element. The mixing element comprises a first steam inlet channel, a necking located downstream thereof and communicating with the first steam inlet channel, having an inner diameter which is smaller than the diameter of the first steam inlet channel, an air inlet channel opening into and communicating with the necking, and a milk inlet channel.
A main channel, also provided in the mixing element, comprises an inlet end and an outlet end, whereby the inlet end communicates with the necking, and whereby the milk inlet channel opens into and communicates with the main channel at a location along the main channel that is downstream the inlet end thereof. Further, the mixing element comprises a second steam inlet channel opening into and communicating with the main channel at a point along the main channel located between the necking and the opening of the milk inlet channel.
Due to the fact that the assembly comprises a mixing element having a central main channel whose inlet communicates with the necking and downstream thereof with the milk inlet channel, whereby a second steam inlet channel opens into the main channel between the necking and the milk inlet channel, even two benefits result: On the one side, the amount of steam available for heating milk can be substantially increased by providing a second steam inlet channel. On the other side, an undesired foaming of the milk can be avoided due to the fact that the above mentioned second steam inlet channel opens into the main channel between the necking and the milk inlet channel, because the steam fed by the second steam inlet channel is not mixed with air that would cause a foaming of the milk.